MINERALS AND GEOLOGY OF CANADA 439 
and on the banks of the stream a little below Paisley. At the mouth 
of the Saugeen, and on the adjacent coast south of this, the forma- 
tion is concealed by Drift sands and clay. 
The gypsum or “ plaster”? deposits constitute the most valuable 
economic material of the Onondaga beds; but some of the dolomitie 
shales of the formation, as those at Walkerton, furnish also valuable 
materials for the manufacture of hydraulic cement. The gypsum is 
principally mined or quarried at Cayuga, Indiana, and York, in the 
township of Seneca; also at Mount Healy and elsewhere in the ad- 
joining township of Oneida, on the opposite side of the Grand River ; 
in Brantford township; and largely around Paris. The annual 
amount obtained at present from these localities, is between fourteen 
and fifteen thousand tons.* 
The Lower Helderberg Group.—The group of rocks thus named, 
is developed somewhat extensively in the vicinity of the Helderberg . 
Mountains and in the eastern part uf New York generally, as well as 
in the more eastern part of Canada south of the St. Lawrence; but 
it thins out towards the west, and presents merely two or three out- 
lying patches in the neighbourhood of Montreal, and a comparatively 
narrow strip of slight thickness in Western Canada, between the east- 
ern end of Lake Erie and the township of Cayuga. It may probably 
extend beyond this latter point along the western limit of the Onon- 
daga zone, up to Lake Huron, but no exposures of its strata have 
been seen west of that township. This strip, in no place exceeding 
fifty feet in thickness, consists of the lowest division of the group 
as subdivided by the New York geologists, or of the equivalents of 
their “ Water-lime Group or Tentaculite Limestone.” With us, in 
Western Canada, it might be called the “ Bertie or Cayuga dolomite,” 
as its only known exposures are in those townships; or a still better 
term would be the Hurypterus formation, so named from its principal 
and characteristic fossil: the Hurypterus remipes, alow form of the 
crustacean class, figured in woodcut 227. In the above townships its 
strata consist of thin-bedded greyish dolomites, interstratified towards 
the base with a few brownish shales, and with a brecciated bed 
composed chiefly of dolomite fragments. 
At St. Helen’s Island and Round Island, opposite Montreal, on 
Isle Bizard, and at one or two neighbouring localities, some outlying 
* The gypsum, as quarried, sells at about $2 the ton. When ground for manure, the cost — 
per ton is about $3.50 ; and when calcined for plaster, about fifteen or sixteen dollars. 
